Various forms of lenses for skylights are known in the prior art. Examples are set forth in U.S. Pat. Nos. 2,693,156; 2,790,400; 3,034,260; 3,127,699; 3,417,527; 4,514,944; and Canadian Pat. No. 689,527. Those references show plastic domes for covering a roof opening, mounted either directly to the roof decking itself or mounted thereto by means of some type of intermediate framing member, such as an upwardly extending marginal curb. Wasserman U.S. Pat. No. 3,127,699 and Kiekhaefer U.S. Pat. No. 3,417,527, for example, teach the use of a double plastic dome having an external or upper member overlying an internal or lower member in peripherally sealed relationship to provide an insulating dead air space therebetween. This is a desirable feature, but the use of plastic as an outer dome material leads to undesirable thermal deformation and/or discoloration.
It is important with such skylight structures to ensure that moisture is kept out of the living space below the skylight structure and also, for double domed structures, to keep moisture out of the dead air space. Various flanging and sealing arrangements exist. There is, however, a continuing problem of providing good sealing against water and moisture intrusion. Where flanges are brought into close contact with adjacent structural members, paths for capillary action movement of water are introduced.
The use of glass lens members for skylight structures is likewise known. These are not readily shapable and are especially undesirable above living spaces because of hazards caused by breakage. They do, nevertheless, offer superiority over plastics in avoiding deformation and other deterioration when acted on by direct hot sunlight.